A number of prior art processes have been proposed for the manufacture of urethanes by reacting hydroxyl group-containing organic compounds, such as alcohols or phenols, with carbon monoxide and certain organic nitro-compounds including the use of catalysts such as certain metal carbonyls, certain complexes of transition metals and noble metal compounds and a Lewis acid.
This invention relates to an improved method for the preparation of urethanes. More particularly, it relates to the preparation of urethanes by reacting an organic nitro-compound, a hydroxyl group-containing compound and carbon monoxide under elevated temperature and pressure conditions in the presence of an effective amount of a catalyst consisting of a mixture of a tertiary organic amine and a platinum group metal or platinum group metal compound.
U.S. Pat. No. 3,338,956 discloses a process for the manufacture of urethanes by reacting a hydroxyl compound, carbon monoxide, and an aliphatic or aromatic nitro-compound at superatmospheric pressures and high temperatures in the presence of a metal carbonyl of elements in groups VIa, VIIa, and VIIIa of the Periodic Table with reaction times ranging from 7 to 18.5 hours.
U.S. Pat. No. 3,454,620 discloses a process for the manufacture of urethanes by reacting an organic compound containing at least one hydroxyl group with carbon monoxide and a nitrogenous organic compound such as nitrobenzene in the presence of a catalyst of complex compound of a platinum group metal and at least one unsaturated hydrocarbon ligand in which the unsaturated system forms a bond with the metal and co-catalyst of a salt of a transition metal.
U.S. Pat. No. 3,467,694 describes a process for preparing a urethane compound by reacting a hydroxy compound, carbon monoxide and an aromatic nitro-compound, at specific molar ratios of carbon monoxide to nitro group, in the presence of a noble metal and a Lewis acid catalyst system. Palladium or rhodium (on-carbon) and the Lewis acid ferric chloride are exemplified and yields of urethane product are not indicated.
The catalyst systems employed in the prior art patents, namely, the metal carbonyls, noble metal/Lewis acid and the platinum group metal/hydrocarbon ligand/transition metal complexes generally require the use of longer reaction times and provide only mediocre yield of urethane product. In addition, the Lewis acid systems present a problem from the standpoint of corrosion, recovery of product and overall handling of reactants.
Many important commercial applications have been developed for the urethane products of this invention, for example, as agricultural chemicals and as chemical intermediates which may be converted to the corresponding isocyanates and alcohols by thermal decomposition or other methods described in the prior art.